Lopez, a psychologist, participates in a defined contribution profit$-$sharing plan with $5-$year graded vesting schedule. Dr$.$ Lopez completed three years of employment but then leaves the company to start a private practice in the middle of the fourth year. If Dr$.$ Lopez had a balance of $$72,000$ in his profit$-$sharing plan at time of separation, what is his vested balance?

Group of answer choices

$$43,200$

$$72,000$

$$0$

$$57,600$